Automated analytical devices and methods capable of performing chemical assays on a series of samples are known in the art. Such devices enable fast, continuous, and reliable analysis of samples for a wide variety of analytes. One type of prior art device includes continuous flow devices which employ polymeric analytical conduits made from TEFLON®, where the conduits include silicone or fluorocarbon oils to preferentially wet the conduit or dispenser surfaces. The use of these materials was found to greatly minimize cross contamination (carryover) of aqueous analytical fluids or streams. These techniques—so called “oil patent” prior art were developed in the mid 1970's and are directed at minimizing sample and reagent cross contamination (carryover) in discrete dispensing operations or continuously flowing streams for high-speed clinical diagnostic testing.
Competing analytical systems, such as those which robotically dispense sample and reagent into various microtiter plate formats and so-called discrete random access clinical analyzers, are also known in the art. These types of systems operate on similar or smaller volume scales at even faster analysis rates and are essentially free of carryover provided that dispensing probes and stirring blades are thoroughly washed between dispensing operations. Because of these advantages, systems of this type have largely supplanted devices based on the “oil patent” technology in commercial applications.
Following is a brief summary of various automated analytical apparatuses and methods described in the art.
U.S. Pat. No. 3,479,141 to Smythe et al. discloses an automated analytical apparatus which transports a plurality of aqueous samples down a flowing stream to a photodetector. The liquid samples may be separated by air segments. According to Smythe et al. inter-sample contamination is successfully reduced by employing a TEFLON® conduit tube, and a liquid carrier medium which is inert and immiscible with the samples. Silicone oil is given as a suitable non-aqueous carrier medium.
In an article entitled “Capsule Chemistry Technology for High-Speed Clinical Chemistry Analyses” by Michael M. Cassaday, et al., Clinical Chemistry, vol. 31, no. 9, 1453-1456 (1985), a continuous flow analytical technique is described where a plurality of micro-aliquots of sample and various reagents are formed in a conduit in the presence of a liquid perfluorocarbon medium. Each sample and reagent micro-aliquot is separated by an air bubble. The presence of the air bubble and the perflourcarbon medium reportedly reduce unwanted sample and reagent carryover. Adjacent micro-aliquot capsules of sample and reagent(s) may be combined to initiate chemical reactions by expanding the diameter of the conduit in a “vanish zone,” so-called because it is designed to remove the air barrier between the capsules allowing the adjacent aliquots to mix. The aliquots then continue through the conduit to a series of in-line reaction detectors, e.g. colorimetric, which are used to quantify the amount of an analyte in a given sample.
U.S. Pat. No. 5,149,658 to Cassaday et al. discloses a method for providing a plurality of discrete samples in a continuous flow analyzer, where the sample aliquots are separated by air and a fine layer of immiscible isolation liquid. The separated samples thus described flow through a conduit which has a sampling probe displaced in the center of the conduit which essentially serves to decrease the amount of isolation liquid separating the samples, yet maintain discrete sample aliquots.
Similar technology is described in PCT International Publication No. WO2005/059512 to Applicant Northeastern University, which relates to a continuous flow analyzer or other microfluidic devices, which can transport a plurality of discrete sample boluses into a micro NMR coil. The device includes a transfer conduit which has an immiscible carrier liquid to prevent the sample bolus from wetting, and thereby contaminating the conduit.
U.S. Pat. No. 4,853,336 to Saros et al. relates to a system of mixing liquid samples with reagents and diluents in a continuous flow analyzer. Similar to the Cassaday publication, the Saros et al. patent is stated to be useful in analytical systems where multi-stage reactions are required. The Saros et al. reference forms discrete sample/reagent section that are separated by air bubbles, where the sample aliquots may be later mixed with additional reagent aliquots by sending the stream through a “vanish zone.”
U.S. Pat. No. 6,623,971 to Adolfsen describes a similar configuration for magnetic particle stat immunoassays. Specifically, as seen in FIG. 4 of the '971 patent, a sample package containing magnetic particles is separated from additional reagents by air bubble and wash aliquots. A magnet transfers the magnetic particles to the additional reagent components which causes photons to be emitted in proportion to the analyte concentration in the sample; the emission is measured by a luminometer. According to the '971 Adolfsen patent, optical carryover between samples is reduced by including a quench package, Q, which terminates the luminescent reaction.
U.S. Pat. No. 5,399,497 to Kumar et al. relates to an automated capsule chemistry system whereby sample packages and reagents are separated by air bubbles and subsequently mixed in a vanish zone. The '497 Kumar et al. reference employs bidirectional pumps such as syringe pumps to aspirate the sample packages and introduce them into the analytical conduit. Similar techniques and devices are also described in U.S. Pat. No. 5,268,147 to Zabetakis et al. and United States Patent Application Publication No. 2006/0172425 to Neigl et al.
Additional references of interest include U.S. Pat. No. 6,613,579 to Wolcot, U.S. Pat. No. 4,520,108 to Yoshida et al, and U.S. Pat. No. 4,224,033 to Hansen et al.
The above approaches, while suitable for analytical operations in medical diagnostics and the like, are impractical for other purposes. For example, the above described techniques require highly complex robotic arms which are used to aspirate the sample and reagent at the tip of the sample needle.
There accordingly exists a need for an automated analytical system that is simple and operable by non-experts, which has low power requirements, and generates small waste volumes—significant hurdles to making an analytical device portable.
Specifically, in the spheres of environmental, industrial, and bioreactor monitoring, there is increasing demand for chemical measurements obtained at higher temporal resolution than can be economically achieved by manual sample collection followed by laboratory analyses. These assessment needs could be met with automatic instrumentation installed at remote locations or in production plants, provided that they were affordable, easy to operate and maintain, and produced data on a par with analytical laboratory results. Typically, in these settings sampling rates of about four per hour to one per day are needed. Sensor technology for water quality parameters such as dissolved oxygen have been improved greatly over the past five years, but progress on sensors for other analytes such as ammonium, nitrate and orthophosphate has been less fruitful. For this reason, most successful automatic water quality monitors still rely on wet-chemical analyses with colorimetric or fluorimetric detection. The cost and complexity of conventional field portable chemical analyzers currently limit their use. Furthermore, the need to replace reagents, perform calibrations, and manage the resulting analytical waste stream has proved particularly problematic for non-specialist operators.
It has been discovered according to the present invention that the above objects can be accomplished by providing an automated analytical system where microliter-sized liquid sample aliquots are introduced into the system and may be positioned to receive various reagents from a dosing module as needed. After the reagent and sample react for the desired time, the aliquot can be positioned to receive additional reagents if needed, or may be conveyed to a detection zone where it is measured for analyte. The apparatus and method described herein enable time-honored wet chemical analyses to be performed on a microliter volume scale with sensor-like simplicity. The apparatus and method further address and solve heretofore intractable problems related to field monitor and industrial process monitor operation and maintenance, power requirements, and waste stream management.
Among other advantages, the present invention (1) is simple and may be operated by non-experts; (2) has very small reagent requirements; (3) generates little waste volume; (4) is virtually immune to optical window fouling; (5) has low electrical power requirements; and (6) is cost effective. Furthermore, it is ideally suited for environmental and process monitoring, and can be made field portable or production-floor portable. These and other features and capabilities of the invention will be made clear in the description which follows and with reference to the accompanying drawings.